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Wheat cultivars and crossbreds with different maturities were tested at a range of sowing times from 1989 to 1991 at 13 sites in the central wheat belt of Western Australia. The aim was to determine if long-season cultivars would allow sowing before mid May, the earliest period estimated by previous studies. Rainfall in the growing season ranged from 176 to 330 mm. Long season cultivars showed the potential to extend the sowing season from early May into late April without loss of yield. Mid-season cultivars reached their maximum yields from sowings in May and short-season cultivars yielded most from late May and early June sowings. The optimum flowering period for the study area over the 3 years was 2-22 September, a period similar to earlier estimates made using only short- and midseason cultivars. It was concluded that, despite considerable variability from year to year both within and between sites, the optimum flowering period did not vary greatly on average and was not greatly affected by the use of long-season cultivars. Sowing after the optimum time resulted in slightly increased grain protein percentages but losses in the value of grain yield would have more than offset increases in the value of grain protein. At the nitrogen rates used in the experiments (80 kg/ha), grain proteins over 11.5% [the minimum for the Australian Hard (AH) grade] were only achieved on average for the long-season AH cultivar Blade at sowing times later than its optimum for yield. The Australian Standard White cultivars, however, mostly achieved 10% protein, an acceptable minimum for that grade, from sowings made at their optimum time. Hectolitre weights fell below the delivery standard of 74 kg/hL in only 3 grain samples. These were all from short-season cultivars sown before their optimum time. Fifteen grain samples from 4 sites contained small grain sievings (2-mm slotted screen) above the delivery standard. Eleven of these samples came from cultivars sown outside their optimum sowing times. |
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